如果数组元素为递增排列，找出数组中的目标值

int binary_search(int num[], int len, int target)
{
    int left = 0;
    int right = len - 1;
    while(left <= right)  //有等于号，才能得到mid
    {
        int mid = (left + right) / 2;
        if(num[mid] > target)
        {
            right = mid - 1;
        }
        else if(num[mid] < target)
        {
            left = mid + 1;
        }
        else
        {
            return mid;
        }
    }
    return -1;
}

int main()
{
    int num[] = {1, 3, 5, 7, 8, 9};
    int mid = binary_search(num, 6, 3);
    cout<<mid<<endl;
    return 0;
}

输出 1。